United Kingdom

Environmental analysis and the challenge for offshore wind developers

UK: Before developers can get on with constructing Round 3 offshore wind farms, a host of environmental surveys must be undertaken to ensure that the turbines within the development zones have minimal impact on the environment, animals and humans.

Turbines at Vattenfall's Thanet wind farm had to be moved after its EIA

Environmental impact assessments (EIAs) are a statutory requirement and apply to all offshore energy developments. An environmental statement - the culmination of dozens of surveys as well as hours of research and analysis undertaken during the EIA process - must form part of a planning application.

EIAs are required for all aspects of the Round 3 offshore wind farms, including the transmission cable route, onshore works such as new substations, as well as the wind turbines. Responsibility for EIAs lies with developers and with offshore transmission owners, separate companies that will manage onshore cable route development.

The surveys are extensive and cover terrestrial, intertidal and subtidal ecology, fish, ornithology, marine mammals, coastal processes, sediment/hydrodynamics, navigation, commercial fishing, archaeology and recreation. Additional geotechnical surveys will be done to inform the engineering design of features such as turbine foundations and cables.

The extensive nature of the EIAs and the larger size of the zones compared to site-specific Round 2 wind farms are a challenge for Round 3 developers. They have to agree methodologies and survey objectives with regulators. They need the right vessels and aircraft for equipment and personnel, and the appropriate range to carry out the surveys.

With nine Round 3 developments starting at around the same time, plus ongoing Round 2 work, there is likely to be a push to secure surveying resources, with delays if there are not enough to go round. And once complete, the survey data has to be analysed and processed into a usable form.

Costly and challenging process

Then there is the unpredictability of the weather. It is not possible to survey in some sea conditions because the equipment does not function correctly or there is a possibility of danger to surveyors. This limits the time available, and the further offshore the development, the harder it becomes to find suitable opportunities to survey.

Finally, cost is a big consideration. Environmental survey costs for a typical 500MW wind farm are in the region of £4 million, according to the Crown Estate.

"The zonal approach to Round 3 is a lot more challenging than site-specific studies for Rounds 1 and 2," says Rob Staniland, technical director of offshore wind at consultancy Royal Haskoning. "The zones are advantageous to developers since they allow more flexibility as to where individual projects can be situated, but the size means companies have a much bigger area to survey and understand."

The EIAs are likely to throw up a number of issues that affect construction plans. These could include evidence of mobile or unconsolidated sediments on the seabed, anomalies such as unexploded bombs or rocky outcrops, or archaeological features such as shipwrecks.

"In many cases it is possible to relocate wind turbines, intra-array and export cabling slightly to avoid sensitive features revealed by surveys," says Dr Tim Norman, senior planning manager at the Crown Estate. "If the feature is more extensive, it may be necessary to revisit the proposed layout."

This happened at Vattenfall's Thanet Offshore Wind Farm, a 300MW Round 2 project. The EIA identified aggregations of the reef-forming Ross Worm (Sabellaria spinulosa). As the turbines could not be situated on these features, there was potential for the loss of generating capacity. The company worked with government agency Natural England on a solution: to relocate affected turbines at least 50 metres from any dense accumulations and to undertake cable burial only when the tide was running away taking with it any harmful suspended sediment.

Developers know that the target of 33GW of offshore wind by 2020 is challenging, and will require hard work, organisation and adequate resources. The start of "surveying season" this spring and summer will be the beginning of a long and detailed process that will define the next generation of offshore wind construction.

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